1. Field of the Invention
The present invention relates to video signal copy-protection technology. In particular, the present invention teaches a method and apparatus for embedding digital data within a video signal such that a television receiver may still produce a normal viewing picture and wherein the embedded digital data may be retrieved by a viewing or recording device, or other hardware.
2. Description of the Related Art
To protect valuable rights in video information, there exists a need for embedding information within a video signal without degrading the signal quality or requiring increased transmission bandwidth, wherein the embedded information may be retrieved by a video receiver system for various purposes. This is increasingly important as large screen, high resolution monitors become widespread, and high picture quality essential. It is also important that such signatures be compatible with digital television processes and components.
Currently standard video broadcast media includes a plurality of field tracks. Each track includes all the video information required for a single TV picture. The beginning of each track includes a vertical blanking interval which is followed by all of the video information for a single TV picture. The NTSC standard has 525 lines of video data in one display picture. However lines 1-21 are not visible. Various data may be stored on any of the lines 1-21, and possibly other lines. Messages embedded into the VBI lines may either be removed intentionally by the equipment used for transmission and reception, or un-intentionally by people who stand to benefit by its removal. E.g. information sent over the XDS channel of line-21 is blocked by most broadcast equipment. Only line-21 CC1 channel has the legal ‘right of support’ in consumer electronics equipment. CC1 channel however, is used for closed captioning and can be displayed on screen. Any non-captioning information sent on CC1 may be viewed by the audience as noisy captions.
Line 21 stores close caption data, while lines 1-20 store other types of information. Line 21 of the VBI is referred to as the CC1 channel of NTSC video signals. Only Line 21 CC1 channel is assigned a protected status by the U.S. and other governments, such that information contained on CC1 of a video signal must be supported by all systems operating in these countries. Any information contained within line 21 will be passed along with video information, and will not be removed.
What is needed is an improved method and apparatus for modifying a video signal so that copying of the modified signal is prevented in a reliable and inexpensive manner, is not easily defeated, yet allows a normal picture to be produced by a television receiver receiving the modified video signal with no impact on picture quality. This invention's goal is to provide a mechanism that embeds data within the CC1 channel of NTSC (or PAL) video signal such that it is non-intrusive to other data or active video, and also is guaranteed legal (regulatory) protection against removal during its transport to the consumer.